Population-based epidemiologic data on non-melanoma skin cancers (NMSCs) remain sparse. In the USA, the last national surveys were conducted in the 1970's. Therefore, in 1993, we established a population-based incidence registry for NMSC in New Hampshire involving a collaborative network of dermatologists and pathologists. Compared to survey data from 1979/80, our findings suggest a dramatic rise in the incidence rates of both basal cell carcinoma (BCC) and squamous cell carcinoma (SCC), and a disproportionate increase in SCC, particularly among women. To understand recent trends in these malignancies, we propose to analyze patterns of BCC and SCC occurrence over a complete decade (1993/94 to 2002/03). These data will permit us to analyze temporal changes in level of invasion and tumor size, indicators of enhanced detection unavailable from prior studies. As part of our study, we established a population-based case-control study of BCC and SCC to identify current risk factors. In the USA and elsewhere, artificial tanning has gained widespread popularity especially among young adults and women. We propose to test the hypothesis that artificial tanning relates to the risk of early onset BCC (age under 50 years at diagnosis) (n about 450) as well as SCC. Based on recent findings, we also will test the hypothesis that prolonged use of photosensitizing drugs enhances risk of SCC (n about 450). In New Hampshire, a growing segment of the population relies on private, unregulated water systems such as bedrock wells (35 to 40 percent currently), and over 10 percent of these contain arsenic concentrations above the present EPA maximum contaminant level of 10 micrograms/L. We propose to examine whether environmental arsenic levels affect risk of multiple BCC (n about 725), a characteristic of chronic high dose exposure. To measure an individual's arsenic exposure, we will test toenail clippings for trace elements and determine drinking water levels from both current and previous households. History of artificial tanning, photosensitizing drug use and other factors will be derived from an in-person interview along with semi-objective and objective assessments. Each case group (multiple BCC, early onset BCC and SCC) will be compared to an age- and gender-matched control group selected from population lists (total n about 1,640). Using the original tumor blocks from NMSC cases, we will perform a histopathology review for diagnostic verification and extent of actinic damage. We will archive both tumor specimens and blood or buccal samples, providing a unique population-based biologic tissue bank for NMSC from which to streamline molecular-epidemiologic investigations.